The present invention relates to a material handling lift vehicle of a type including a vertical mast at one end, vertical travel of a carriage along the mast being effected by vertical movement of a lever arrangement upon the vehicle which preferably comprises an overhead guard structure for an operator station.
Many designs are known in the prior art for lift vehicles of a type generally contemplated by the present invention. In most such conventional lift vehicles, a material handling carriage is arranged for vertical travel along a vertical mast including at least a fixed upright. In many designs, a mast assembly includes one or more movable uprights which may be raised to serve as extensions for the fixed upright with the carriage being movable along the entire extended length of the mast assembly.
The most conventional arrangement for such mast assemblies includes a hydraulic jack which serves both to cause free travel of the carriage along the mast and also to shift the movable uprights into their extended positions. The movable uprights are commonly positioned by means of chains which are secured to one portion of the fixed upright and trained about sheaves on the movable uprights, operation of a single jack commonly being employed to effect both free travel of the carriage and extension of the movable uprights.
Additional lift vehicles are also known in the prior art having material handling carriages which may be freely supported by one or a pair of elongated levers arranged along the length of the vehicle. Normally, the carriage has a fixed pivotable mounting on the levers and remains connected to a movable end of the levers. It is desirable to have such carriages travel in a straight vertical line rather than along an arcuate path as would normally be provided by such a lever configuration. Accordingly, relatively complicated linkages are provided for the levers in order to compensate for its normal arcuate path and produce a more vertical straight line path of travel for the carriage. Lift vehicles of the type described immediately above may be seen for example in U.S. Pat. Nos. 2,980,271; 3,187,911; 3,198,359; 3,432,050; and 3,454,176.
However, it has been found that there remains a need for a relatively simple and effective material handling lift vehicle of a type including an operator's station with a carriage being arranged for vertical travel along a mast at one end of the vehicle.